Millimeter wave signals are used for radar and telecommunications. They are also capable of being used to produce an image of a subject by directing millimeter-wave signals at the subject and detecting the reflected signal. Examples of such imaging systems are described in U.S. Pat. Nos. 5,455,590; 5,557,283; 5,859,609; 6,507,309; 6,703,964; 6,876,322; and 7,034,746; U.S. Patent Application Publication Numbers 2004/0090359, 2004/0140924, 2006/0066469, and 2007/0075889; and U.S. patent application Ser. No. 11/088,470 filed Mar. 24, 2005. The complete disclosures of the above patent references are herein incorporated by reference for all purposes.
Imaging systems, including those systems described above, provide relatively detailed images of a subject, including a person's body and any objects carried by the person, whether or not the objects are concealed. An operator can view images of a subject and visually identify objects included with the person. Other detection devices can also be used to obtain other information about a subject. For instance, the subject can pass through a metal detector to determine if the subject has a detectable metal object.
Additionally, or alternatively, the surveillance system may include imaging systems and/or other detection devices to obtain information about subject-associated items, such as divested objects, checked baggage, and carryon baggage. For example, imaging systems may be used to produce images of checked baggage. An operator can view images of checked baggage and visually identify objects included with that baggage. Other detection devices can also be used to obtain other information about subject-associated items. For example, trace detection devices may be used to determine if the subject-associated item has an explosive substance or an illegal drug.
When the surveillance system is part of a process of boarding a public transportation vehicle, or entering a public or protected facility, substantial delays may be realized. Further, the effectiveness of the surveillance depends on the accuracy and attentiveness of the operator or operators.